code: def demo_read_depgraph():
      from nltk.parse.dependencygraph import DependencyGraph
  
      dg1 = DependencyGraph(
          """\
  Esso       NNP     2       SUB
  said       VBD     0       ROOT
  the        DT      5       NMOD
  Whiting    NNP     5       NMOD
  field      NN      6       SUB
  started    VBD     2       VMOD
  production NN      6       OBJ
  Tuesday    NNP     6       VMOD
  """
      )
      dg2 = DependencyGraph(
          """\
  John    NNP     2       SUB
  sees    VBP     0       ROOT
  Mary    NNP     2       OBJ
  """
      )
      dg3 = DependencyGraph(
          """\
  a       DT      2       SPEC
  man     NN      3       SUBJ
  walks   VB      0       ROOT
  """
      )
      dg4 = DependencyGraph(
          """\
  every   DT      2       SPEC
  girl    NN      3       SUBJ
  chases  VB      0       ROOT
  a       DT      5       SPEC
  dog     NN      3       OBJ
  """
      )
  
      depgraphs = [dg1, dg2, dg3, dg4]
      for dg in depgraphs:
          print(FStructure.read_depgraph(dg))
  
file_path: nltk/nltk/sem/lfg.py
imports: from itertools import chain
  from nltk.internals import Counter
label_desc: Use image node_id 1 for calling a global function with example usage: demo_read_depgraph() without return types